External bone distractor

ABSTRACT

The invention relates to an external bone distractor ( 1 ) of the type that consists of: a threaded curvilinear rod ( 4 ) comprising several diametrical flat sections ( 7, 8 ) with the thread ( 9 ) of said rod ( 4 ) continuing along longitudinal lines; at least two carriages ( 2 ) which are engaged on said rod ( 4 ) and which are solidly connected to spindle supports ( 3 ); guide means ( 10, 13 ) which co-operate with said flat sections ( 7, 8 ) in order to prevent the rotation of each of the carriages ( 2 ) around the axis of the rod ( 4 ); and means for adjusting ( 14, 15 ) the position of each of the carriages ( 2 ) along the length of said rod ( 4 ). The inventive external bone distractor is characterised in that the rod ( 4 ) thereof is curvilinear in shape. Said distractor is suitable for use in the reconstruction of curved bone segments, particularly in the jaw, face and skull.

TECHNOLOGICAL BACKGROUND TO THE INVENTION

The replacement of a missing bone fragment following resection of atumour or major trauma often uses operating techniques designed topromote the growth or development of the adjacent healthy section ofbone tissue.

One of these comprises exerting tension on the bone callus resultingfrom an osteotomy in order to lengthen it by an amount corresponding tothe bone loss.

This technique, which has been considerably developed by the Russianpractitioner Ilizarov, was initially used for the long bones or at leastfor bone fragments of generally cylindrical shape.

The external distractor described by this author in U.S. Pat. No.4,978,348 published on 18 Dec. 1990 appears to offer sufficientflexibility of use to enable it to be used both for restoring the shapeof the hand, by stretching the parts of phalanges remaining afteramputation, and for the reconstruction of the mandible, for example.

The system comprises a set of threaded rods which may be assembled tofit the shape of the bone or set of bones being treated. The threadedrods carry pin-supporting carriages the adjustable spacings of whichallow the bone distraction to take place. The pins of each carriage aretightened by a nut between washers threaded onto a hollow bolt engagingon one of the rods. The latter have a flat section cooperating withgudgeons of the hollow bolts for securing the pin supports againstrotation relative to the rods.

The apparatus is simple but, as the carriages are held in place on therods by locknuts, two spanners are needed to move them. Moreover, thelocking and unlocking of a locknut requires a relatively complexsimultaneous manipulation of these two spanners.

The external osteosynthesis fixator disclosed in Utility CertificateApplication FR 2,671,479 in the name of the company Hit Medica,published on 17 Jul. 1992, is based on the principle of the turnbuckle.The two spindle supports are thus simply moved apart by manipulating thecentral part of the rod, the ends of which are threaded in oppositedirections.

Based on another principle, the apparatus described in U.S. Pat.4,848,368 published on 18 Jul. 1989 in the name of R. Kronner canaccording to the applicant be manoeuvred using a single knurled wheel.In this case the patient himself can perform the task.

The two systems mentioned above may be used for the distraction ofstraight bones, be they long or short, but they are not suitable forcurved bones such as, for example, the bones of the skull, the mandiblesor the ribs.

An apparatus which is specially adapted for the curved bone segments ofjaws, face or cranium is described in German Patent Application DE 19503 609 published on 10 Aug. 1995 in the name of Messrs Normed MedizinTechnik Vertriebs. The apparatus is formed from a plurality of racks onwhich pin-supporting carriages are fixed. The racks are articulated toone another so that the assembly fits the shape of the bone on theoutside. A carriage can be moved along a rack using a screw engagingtherewith.

The joints between the racks comprise spherical connections, which hasthe advantage of allowing the assembly to be made in any shape. However,these joints have the serious disadvantage of restricting the movementof the carriages.

A threaded, curved, continuous rail which does not limit the movement ofthe pin-supporting carriages is disclosed in Japanese Patent ApplicationJP 09-215699 published on 19 Aug. 1997 in the name of Messrs NagoyaRashi Seisakusho.

According to the embodiment shown in the Figures accompanying theapplication, the rail has a square cross section and is threaded on eachof its edges. In the example of use described, the rail is fixed to theright-hand side of a mandible and follows the contour thereof, from backto front, without going past the start of the chin.

However, it appears technically impossible for the rail described in JPapplication 09-215699 to follow the contour of the mandible beyond thestart of the chin. The small radius of curvature at the chin wouldobviously result in a substantial deformation of the threads of the rodand prevent the rotation of the nuts which control the movement of thecarriages.

In fact, in the position shown in the drawings which accompany JPapplication 09-215699, the threads inside the curve followed by the rodare necessarily compressed, while the outer threads are moved apart.

As a result, the curved rail would appear to be usable only forrepairing a side part of the mandible, as shown in the main Figure, andcertainly not for distraction of the median part of the mandible.

Consequently, it is apparent from the prior art as described in thedocuments cited above that external bone distractors adapted for thereconstruction of curved bone segments, notably the bones of the jaw,face and cranium, are known, but at present there is no osteogenicdistraction device which has features that fully meet the needs ofmaxillo-facial surgery.

GENERAL DESCRIPTION OF THE INVENTION

The present invention therefore relates to an external bone distractorcomprising in known manner:

-   -   a threaded curvilinear rod comprising a plurality of        diametrically opposed flat sections, preserving the threading of        the rod along longitudinal bands,    -   at least two carriages engaging on said rod and solidly attached        to pin supports,    -   guide means which co-operate with said flat sections in order to        prevent the rotation of each of the carriages around the axis of        the rod,    -   means for adjusting the position of each of the carriages along        the rod.

The invention specifically relates to a distractor of this type theessential feature of which is that the longitudinal bands along whichthe threads are preserved extend solely in the vicinity of the neutralfibres of the rod.

According to an additional feature of the distractor according to theinvention there are only two of these longitudinal bands and they arediametrically opposed.

Preferably, the rod, more simply, forms a curved plane.

Advantageously the curve formed substantially fits the shape of themandible. It is preferably made up of a 150° arc of a circle, the endsof which are extended by two straight segments.

In one particular embodiment of the distractor, the threaded rod has sixdiametrically opposed flat sections machined so that the sides of thestraight section of the rod, and their extensions, adjacent to the linesof the neutral fibres, form a square.

Preferably, the guide means comprise at least one washer solidlyattached to each of the carriages engaging on the rod by means of anaxial bore the section of which is complementary to the cross section ofsaid rod.

According to an alternative embodiment of the external bone distractoraccording to the invention these guide means comprise at least one pairof dual wheels the rotation axles of which are firmly attached to thoseof the carriages, arranged to straddle the rod on either side androlling on said rod.

As for the adjustment means, these preferably comprise a knurled nutscrewed onto the rod acting on each of the carriages by means of abracket.

Advantageously the guide means for a carriage have two positions: thedirection of the pin support in one of the positions is perpendicular tothe direction of the pin support in the other position.

There is an advantage in the fact that at least two of the carriages ofthe external bone distractor according to the invention are fixed andthat a third is movable along the rod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 3 and 4 diagrammatically show the bone distractor according tothe invention viewed from below, from in front and from the left,respectively.

FIG. 2 shows an enlarged cross section through the threaded rod whichforms part of the distractor according to a preferred embodiment of theinvention.

FIGS. 5 a and 5 b show a first embodiment of one of the pin-supportingcarriages of the distractor according to the invention viewed from aboveand from the front, respectively.

FIGS. 6 a and 6 b show an alternative embodiment of one of thepin-supporting carriages of the distractor according to the invention,with the cover removed, viewed from above and from the front,respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The references to FIG. 1 and FIG. 2 will serve to explain the generalprinciple of the invention by describing a model apparatus adapted tojaw reconstruction by progressive bone distraction.

FIG. 1 is a simplified view of the distractor 1 from below. Carriages 2are shown, supporting pin supports 3 engaging on a threaded rod 4.

Unlike known devices comprising one or more straight rods, this threadedrod 4 is continuous and its shape substantially fits the outer shape ofthe jaw.

It has a front section 5 in the shape of a 150° arc of a circle with aradius of 70 mm, and two side sections 6 consisting of straight segments90 mm long.

FIG. 2 clearly shows in section (section AA) the other essential featureof the threaded rod 4. Six flat sections 7,8 formed in a threaded rod toISO standard M6 preserve the threading 9 only in the vicinity of theneutral fibres of the rod 4, i.e. the fibres of the rod 4 which are notsubjected to extension or compression and which are therefore located inthe vicinity of each of the two planes at a tangent to the rod 4 whichare parallel to the plane in which said rod extends. Each preserved part9 of the thread thus retains the nominal characteristics of the profileof the threads and of the pitch of the threaded rod 4 and canconsequently co-operate with a nut of the corresponding size. This nut,as will be explained in connection with FIGS. 5 and 6, will constitute ameans of adjusting the position of a carriage 2 along the rod 4.

As shown in FIGS. 3 and 4, the carriages 2 are capable of holding thepin supports 3 either in a position which is perpendicular to the planeof the distractor 1 (carriages 2 on the front section 5), or in aparallel position (carriages 2 on the side sections 6).

To do this, the carriages 2 are guided on the rod 4 and secured againstrotation thereon by guide means adapted to the particular shape of thesection (FIG. 2) of the threaded rod 4

The sides 7 of this straight section adjacent to the preserved parts 9of the thread in the vicinity of the neutral fibres, and the extensionsthereof, in fact form a square BCDE.

In a first preferred embodiment of the distractor 1, a carriage 2 isintegral with two aligned washers 10 the axial bore 11 of which issquare in section, as is clearly shown in FIG. 5 b, i.e. complementaryto the rod 4 on which they are engaged. The carriage 2 can thereforeslide along the threaded rod 4 but has only two positions of axialrotation, at 90° to one another, depending on the manner in which it hasbeen threaded on the rod 4.

According to an alternative embodiment shown in FIGS. 6 a and 6 b, thechannel 12 of square section in which the threaded rod 4 travels insidea carriage 2 is obtained by means of two pairs of aligned dual wheels13. The dual wheels 13 rotate in four cylindrical recesses in the bodythat constitutes the carriage 2, thus allowing the threaded rod 4 toslide while being guided.

The carriage is shown with the “cover removed”, so as to allow thesedual wheels 13 to be seen in FIG. 6 a.

As before, the carriage 2 may be oriented on the rod in two differentways.

The free space left in the body of the carriage 2, between the washers10 or the dual wheels 13, for accommodating a knurled nut 14 screwedonto the rod 4, forms a bracket 15 which transmits the movements of thisnut 14 to the carriage 2.

The nut can easily be manipulated by the patient himself. A ratchetindicates the number of fractions of a turn made.

Cylindrical bores 16 are provided in the body of the carriages forreceiving the rods of the pin supports 3, which are irmmobilised byscrews.

These very lightweight and very simple structures of the carriages 2,according to the views of the distractor 1 according to the inventionshown in FIGS. 1, 3 and 4, therefore enable the pins 17 to be placedideally at the most favourable points on the jaw to produce the desiredbone distraction without any problems.

The travel profile of the carriages 2, ideally suited to the shape ofthe jaw, makes the distraction particularly progressive.

It will be appreciated that the rod 4 acting as a rail must be keptfirmly attached to the jaw by the pins of at least two fixed carriages2. At least a third carriage is movable to allow the movement of thebone.

The advantages of the curved shape of the threaded rod 4 are easilytransposed to cases other than the jaw; a rod of suitable size and shapefor the skull would constitute the basis of an apparatus for distractingthe cranium.

It goes without saying that the invention is not limited to just thetechnical specifications described above by way of example; on thecontrary it includes all the other possible alternative embodiments.

In particular, the guide means 10, 13 for the carriages 2 or the meansfor regulating their positions 14 described above are not restrictive.Any other mechanical means used for the same purposes constitute apossible variant which does not go beyond the inventive concept of theexternal bone distractor the features of which are specified below.

1. An external bone distractor (1) comprising: a threaded curvilinearrod (4) comprising a plurality of diametrically opposed flat sections(7, 8), preserving the threading (9) of the rod (4) along longitudinalbands, at least two carriages (2) engaging on said rod (4) and solidlyattached to pin supports (3), guide means (10, 13) which co-operate withsaid flat sections (7, 8) in order to prevent the rotation of each ofsaid carriages (2) around the axis of said rod (4), means (14, 15) foradjusting the position of each of said carriages (2) along said rod (4),characterised in that said bands extend solely in the vicinity of theneutral fibres of said rod (4).
 2. An external bone distractor (1)according to claim 1, wherein there are only two bands (9) and they arediametrically opposed.
 3. An external bone distractor (1) according toclaim 2, wherein the rod (4) forms a flat curve.
 4. An external bonedistractor (1) according to claim 3, wherein the rod (4) forms a curvewhich substantially fits the shape of the jaw on the outside, preferablymade up of a 150° arc of a circle (5), the ends of which are extended bytwo straight segments (6).
 5. An external bone distractor (1) accordingto claim 4, wherein the rod (4) has six diametrically opposed flatsections (7, 8) machined so that the sides of the straight section (AA)of said rod (4), and their extensions, adjacent to the lines of theneutral fibres (9), form a square (BCDE).
 6. An external bone distractor(1) according to claim
 1. wherein the guide means (10, 13) comprise atleast one washer (10) solidly attached to each of the carriages (2),engaging on the rod (4) by means of an axial bore (11) of complementarysection to the straight section (AA) of said rod (4).
 7. An externalbone distractor (1) according to claim 5, wherein the guide means (10,13) comprise at least one pair of dual wheels (13) the rotation axles ofwhich are integral with those of the carriages (2), arranged so as tostraddle the rod (4) on either side, and rolling thereon.
 8. An externalbone distractor (1) according to claim
 1. wherein the adjusting means(14, 15) comprise a knurled nut (14) screwed onto the rod (4) acting oneach of the carriages (2) via a bracket (15).
 9. An external bonedistractor (1) according to claim
 1. wherein each of the guide means(10, 13) has two positions, the direction of the pin support (3) in oneof said positions being perpendicular to the direction of the pinsupport (3) in the other said position.
 10. An external bone distractor(1) according to claim 1, wherein at least two of said carriages (2) arefixed, and at least a third is movable along the rod (4).